1. Field of the Invention
The present invention relates to a projection image display device that projects an image onto a screen and more particularly to cooling of the projection image display device.
2. Description of the Background Art
Conventionally, many projection image display devices (projectors) adopt lamps as light sources for generating light beams of three primary colors. These projection image display devices separate white light emitted from the lamps, into the three primary colors of red (R), green (G), and blue (B) by means of a dichroic mirror, and after modulating the three primary colors by image information and combining them by a combining prism, the projection image display devices project them onto a screen through a projection lens, to thereby display an image.
On the other hand, demands for higher-luminance (higher output power), a wider range of color reproduction, and a longer life have been increasing recently. However, promoting higher-luminance of the projection image display devices including the lamp light sources as described above is difficult in terms of an increase in heat generation and noise as well as an increase in size of a cooling structure and a power supply, and furthermore the wider range of color reproduction and the longer life are also difficult to be achieved.
Thus, in place of the lamp light sources, a semiconductor laser element and a light emitting diode (LED) that have a wide range of color reproduction and have a long life are being used as light sources. Moreover, the plurality of semiconductor laser elements and the plurality of LEDs are used as light source elements, so that developments of light sources capable of high output power and projection image display devices provided with the light sources are also promoted.
In the projection image display device using the semiconductor laser elements or the LEDs, for light emission and oscillation of the semiconductor laser elements or the LEDs of each color (R, G, B) with stability, their operating temperatures are needed to be maintained constant, which leads to an important task.
Particularly, in a case where the light source elements are the semiconductor laser elements, an efficiency of light emission increases as the operating temperature decreases, and on the other hand, as the operating temperature increases, the efficiency of light emission decreases and an increase in crystal defects also progresses. Moreover, an increase in heat generation corresponding to an increase in a non-radiative transition accompanied by the progression may further cause a temperature rise of a light-emitting element and accelerated decline of its light-emitting capability may occur. In addition, a shortening of life may progress rapidly. Furthermore, no matter how high or low an operating temperature is, a wavelength of an output light changes correspondingly to the operating temperature, whereby the original color and the image cannot be projected.
Thus, in a case where the light source elements are the semiconductor laser elements, it is important to maintain the operating temperature at a constant optimum temperature.
The conventional technique for stabilizing the operating temperature of the semiconductor laser elements is a cooling technique using a Peltier device. However, an air-cooled cooling is generally used for exhaust heat of the Peltier device, and a heat pipe, a heat sink, a fan, and the like in large size are needed to achieve a sufficient cooling capability by the air-cooled cooling for high output power, resulting in problems that a size of the device and noise by the fan increase. A loss of power by the Peltier device is large, and thus it is conceivable that power consumption is large and efficiency is poor.
Moreover, a cooling technique using a water cooling is another cooling technique, but due to a temperature differential between an upper stream and a lower stream, maintaining the operating temperature of the plurality of semiconductor laser elements constant is difficult.
As another cooling technique, for example, Japanese Patent Application Laid-Open No. 2009-222869 discloses the technique for supplying an optical element group with air that has exchanged heat to cool the optical element group. However, a volume of cooling air for the optical element group is unbalanced, and thus it is difficult to maintain the operating temperature constant. The technique disclosed in Japanese Patent Application Laid-Open No. 2009-222869 also requires a large fan for cooling, resulting in problems that a size of the device and noise by the fan increase.
In Japanese Patent Application Laid-Open No. 2009-42703, to solve the problems as mentioned above, the technique for using a refrigerant circuit including, for example, a refrigerant compressor, a condenser, a fan, a pressure reducer, and an evaporator (or a heat sink) to cool a semiconductor laser element by vaporization and latent heat of a refrigerant has been developed.
The technique of Japanese Patent Application Laid-Open No. 2009-42703 can maintain an operating temperature constant. However, as in the technique of Japanese Patent Application Laid-Open No. 2009-42703, in a projection image display device in which a circuit for projecting an image and a refrigerant circuit are integrated, sizes and weights of a compressor, a condenser, a fan, and a power supply increase as a high output is produced. Thus, size of a space for installing the projection image display device and load capacity thereof lead to a problem, resulting in an increase in cost of installation. Moreover, it is a problem that noise caused by upsizing of the fan or the compressor also increases.